Portable wireless unit

ABSTRACT

A portable wireless unit of the invention has a first plane antenna smaller than an antenna size determined by a desired frequency, and a second plane antenna presenting an antenna size determined by the desired frequency on the whole by coupling with the first plane antenna.

FIELD OF THE INVENTION

[0001] The present invention relates to a portable wireless unit, andmore particularly to aportable wireless unit, e.g. cellular phone, usinga plane antenna such as plate-form inverted F type antenna.

BACKGROUND OF THE INVENTION

[0002] Most of handy-type portable wireless units used in a gigahertzband are provided a whip antenna that is accommodated in the case, or aplane antenna such as a plate-form inverted F type antenna that is builtin the case.

[0003]FIG. 1 shows a cellular phone, which is one of the conventionalportable wireless units.

[0004] In a case 61, a circuit board 62 mounting the transmission andreception circuit (not shown) is accommodated, and numeric keys,function keys and liquid-crystal display (neither shown) are provided onthe front side (backside of the case 61 in the drawing) of the case 61formed by resin molding, and a whip antenna 63 (for transmission andreception), which can be retracted in the case 61, in flexible structureis disposed in the upper part of the case 61. A plate-form inverted Ftype antenna 64 is disposed in the vicinity of the backside wall of thecase 61. The plate-form inverted F type antenna 64 comprises a radiationplate 64 a and a short-circuit plate 64 b that is formed in part of theradiation plate 64 a and soldered to the earth land or shield plate ofthe circuit board 62. A power feed wire 65 is connected to a givenposition of the radiation plate 64 a.

[0005] As is generally known, the plate-form inverted F type antenna 64is designed to satisfy an expression, L=W·λ/4, where the length of theradiation plate 64 a is L, the width is W, and the wavelength is λ. Italso has a characteristic that the bandwidth widens as the interval h ofthe radiation plate 64 a and earth land or ground plate increases, andthe efficiency (gain) lowers as the volume of the case (casing)decreases.

[0006] In the portable wireless unit in FIG. 1, the combination of theplate-form inverted F type antenna 64 and the whip antenna 63 composes adiversity antenna, thereby the multi-path fading can be decreased.

[0007] In the conventional portable wireless unit, however, if attemptedto use a portable wireless unit accommodating the antenna (planeantenna) at a desired service frequency (hereinafter called desiredfrequency), the antenna needs to have a size according to the designvalue. Therefore, there occur problems that it becomes difficult toinstall its internal parts inside the case, it becomes difficult to getthe sufficient frequency band, and the radiation efficiency (antennaefficiency) is likely to lower. In addition, there is a problem that thecase space cannot be used efficiently.

[0008] To solve these problems, reported is, for example, Arai et al.,“Structural method of unidirectional antenna for portable terminal andphantom effect of human body”, the general meeting of Institute ofElectronics and Communication Engineers of Japan, SB-1-12 (1999). Thispaper reports a technology for obtaining two-resonance characteristic byoperating an exciting element at a desired operation frequency. But itspurpose is only to obtain the two-resonance characteristic, and it isnot possible to improve the lowering of radiation efficiency caused bythe space in the case.

SUMMARY OF THE INVENTION

[0009] It is an object of the invention to provide a portable wirelessunit capable of enhancing the antenna characteristics, while reducingthe occupied area in the case, by using an incorporated antenna such asplane antenna.

[0010] To achieve the object, the invention provides a portable wirelessunit comprising a first plane antenna smaller than an antenna sizedetermined by a desired frequency, and a second plane antenna presentingan antenna size determined by he desired frequency on the whole bycoupling with the first plane antenna.

[0011] According to this constitution, the first plane antenna andsecond plane antenna do not exhibit the resonance functionindependently, but the first and second plane antennas function toresonate at the desired frequency on the whole. The first plane antenna,when coupled with the second plane antenna, is lowered from theresonance frequency at the desired frequency. Accordingly, the firstplane antenna is set smaller than the antenna size determined by thedesired frequency, and is hence raised in the resonance frequency. Thus,since the antenna size of the first plane antenna is smaller than in thecase of the resonance frequency at desired frequency (frequency oftransmission and reception), the occupied area of the antenna in thecase is smaller, and the space in the case can be utilized effectively.Further, by coupling of the first plane antenna and second planeantenna, the effective antenna area can be increased, and the occupiedarea of antenna in the case is smaller, so that the antennacharacteristic can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a perspective view showing an example of a conventionalportable wireless unit.

[0013]FIG. 2 is a perspective exploded view showing an embodiment of aportable wireless unit of the invention.

[0014]FIG. 3 is a diagram showing the portable wireless unit of FIG. 2after assembled, in which (a) is a plan and (b) is a side sectionalview.

[0015]FIG. 4 shows a specific example of a plane antenna of theinvention, in which (a) is an example of a plate-form inverted F typeantenna, (b) is an example of a microstrip antenna, and (c) is aperspective view showing an example of a chip antenna.

[0016]FIG. 5 shows other embodiment of a portable wireless unit of theinvention, in which (a) is a plan, and (b) is a side sectional view.

[0017]FIG. 6 is a perspective view showing an embodiment of a planeantenna type in FIG. 4 (a).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Preferred embodiments of the invention are described below whilereferring to the accompanying diagrams.

[0019]FIG. 2 and FIG. 3 show an embodiment of a portable wireless unitof the invention. In FIG. 2, main parts are shown in disassembled state,and FIG. 3 shows an assembled state, in which (a) is a plan and (b) is aside sectional view.

[0020] The case forming the casing is composed of an upper case 1 and alower case 2 of plastic molding, and between the upper and lower cases,there is a circuit board 4 mounting a plane antenna 3 (a first planeantenna) as an excitation element. The circuit board 4 has a multi-layerstructure, and the surface of one side forms a grounding plane. Theplane antenna 3 is connected directly to the transmission circuit of thecircuit board 4, and is excited at a desired frequency (=frequency oftransmission and reception, for example, 2 GHz), and its resonancefrequency is set at a higher frequency than the desired frequency, andhas a narrow band characteristic. The reason of such setting of higherresonance frequency and narrower band is because a parasitic element 5is provided as a second plane antenna as described below. Since theplane antenna 3 has a higher resonance frequency than the desiredoperation frequency, its antenna size is smaller than that at thedesired operation frequency.

[0021] Confronting the plane antenna 3, the parasitic element 5 made ofcopper plate or other metal plate is placed on the outer surface of theupper case 1. The parasitic element 5 is disposed at a position overlaidin part or whole on the plane antenna 3. Its antenna size is set at avalue for obtaining a resonance frequency equal to the desired frequency(frequency of transmission and reception) at the time of excitation ofthe plane antenna 3. In this case, the higher the resonance frequency ofthe plane antenna 3, the larger is the size of the parasitic element 5,and the lower the resonance frequency of the plane antenna 3, thesmaller is the size of the parasitic element 5. The parasitic element 5is a radiation source for radiating radio waves, and the plane antenna 3functions as an excitation source for resonating the parasitic element 5at a desired frequency.

[0022] Since a desired frequency is obtained by exciting the planeantenna 3 at higher frequency than the desired frequency, the relationbetween the plane antenna 3 and parasitic element 5 is in tuning andcoupling relation, and it is considered that the parasitic element 5becomes a load to the plane antenna 3 to lower the impedance. By thepresence of the parasitic element 5, as seen from the plane antenna 3reduced in size, the effective antenna area is increased (that is, it isthe same effect as when the size of the entire antenna is increased, andthe resonance frequency of the entire antenna is lower than theindependent resonance frequency of the plane antenna 3).

[0023] Hitherto, in order to achieve two-resonance or wider band, aparasitic element is disposed opposite to a current feeding element, asdescribed, for example, in “Mobile Communication Handbook” (T. Saito, K.Tachikawa, p. 126, FIG. (f), Ohm-Sha). In this case, too, the sizes ofthe current feeding element and parasitic element are set at differentsizes according to two frequencies or bands desired to be obtained.Unlike this invention, it is not intended to obtain one resonancefrequency, and the size of the current feeding element (plane antenna inthe invention) is set to one frequency of two-resonance, or thefrequency at the upper limit side or lower limit side of the band. Inthe invention, by contrast, the size of the plane antenna 3 is set so asto resonate at a higher frequency than the desired frequency, and whenthe parasitic element 5 is coupled, it is designed so that [planeantenna 3+parasitic element 5] may resonate at a desired frequency asone antenna, which is a major difference from the prior art.

[0024] Further, although not shown in the drawing, the liquid crystaldisplay and key block are installed at specified positions on the uppercase 1. Moreover, as required, a whip antenna as shown in FIG. 6 isinstalled at a specified position of the upper case 1.

[0025] Thus, pairing with the plane antenna 3, the parasitic element 5is provided on the upper case 1, and the parasitic element 5 is excitedby the plane antenna 3, and this parasitic antenna 5 is used as theradiation source. Since the resonance frequency of the plane antenna 3can be set higher than the intended operation frequency, the size of theplane antenna 3 can be reduced. Hence, the occupied area in the case isreduced, and the effective antenna area can be increased by combinationwith the parasitic element 5.

[0026] As a result, the plane antenna is reduced in size, and the areaof the circuit board 4 may be smaller, and the portable wireless unit issmall and light, and the space for accommodating other parts can beincreased. Since the plane antenna 3 and parasitic element 5 resonate ata desired frequency as one antenna, the antenna characteristics(frequency band, radiation efficiency, etc.) can be enhanced. Further,since the parasitic element 5 is not supplied with current, the currentfeeding wire to be connected to the circuit board 4 is not needed, andthe manufacturing process is not complicated.

[0027]FIG. 4 shows a specific example of the plane antenna 3.

[0028] In FIG. 4(a), a plate-form inverted F type antenna explained inFIG. 6 is used as the plane antenna 3. A plate-form inverted F typeantenna 31 comprises a radiation plate 31 a, a spacer 31 b made ofdielectric (or non-dielectric) material for positioning the radiationplate 31 a on an earth land 32 of the circuit board, a current feedingunit 31 c connected to the output terminal of the circuit board 4disposed through this spacer 31 b, and a short-circuit board 31 d forconnecting a part of the radiation plate 31 a and the earth land 32.

[0029] In FIG. 4(b), a microstrip antenna 33 is used as the planeantenna 3, and it comprises a band-like radiation plate 33 a formed of amicrostrip line on an insulator, and a pair of spacers 33 b, 33 c forholding this radiation plate 33 a on the earth land 32 of the circuitboard.

[0030]FIG. 4(c) shows an example of using a chip antenna 34 as the planeantenna 3. The chip antenna 34 is made of a dielectric material as thebase material, and a pair of electrodes are integrated on the dielectricmaterial as an antenna element. This chip antenna 34 is fixed on theearth land 32 of the circuit board, and comprises a current feedingterminal 34 a connected to the current feeding unit of the circuit board4, and a grounding terminal 34 b connected to the earth land 32.

[0031]FIG. 5 shows other embodiment of the portable wireless unit of theinvention. In FIG. 5, (a) is a plan, and (b) is a side sectional view.

[0032] In this embodiment, the parasitic element 5 is disposed at theconfronting position of the plane antenna 3 on the inner wall of theupper case 1. This embodiment is suited to the case in which there is asufficient space in the case, or the thickness of the case is permitted,and since the parasitic element 5 is protected by the upper case 1, itdoes not require a partial cover for protecting the parasitic element 5,or a decorative member for improving the appearance.

[0033] In FIG. 5, according to a structure of projecting the parasiticelement 5 from the inner surface of the upper case 1, it may be buriedin the upper case 1, and the inner surface of the upper case 1 may be 5flat.

[0034] [Embodiment]

[0035]FIG. 6 shows an embodiment of a plane antenna type of FIG. 4(a) Aplane antenna 51 comprises a radiation plate 51 a disposed on thesurface of the upper case 1, a folding part 51 b formed by folding andbending to one side of the radiation plate 51 a, short-circuit plates 51c, 51 d formed at other side of the radiation plate 51 a, and a spacer51 e for insulating and holding the folding part 51 b. The folding part51 b is provided for forming an electrostatic capacity, and theshort-circuit plates 51 c, 51 d function as the stabs for determiningthe resonance frequency.

[0036] The dimensions of the parts in the case of desired frequency of 2GHz are as follows: the circuit board 4 measures 120 mm×35 mm, theradiation plate 51 a is 10 mm in length L and 7 mm in width W, theheight H of the short-circuit plates 51 c, 51 d is 5 mm, the horizontalplane length d of the folding part 51 b is about 7 mm, and the thicknesst of the spacer 51 e is 1 mm. The resonance frequency of the planeantenna 51 differs depending on the interval and relative position tothe parasitic element 5, and mounting state of other parts, but it isgenerally about 1.5 times of the desired frequency (2 GHz herein).

[0037] On the other hand, the parasitic element 5 is a copper plate of20 mm in width and 60 to 70 mm in length, and its resonance frequency isabout 3 to 5 GHz ideally, but it varies depending on the interval andrelative position to the plane antenna, and mounting state of otherparts, and hence it is determined experimentally.

[0038] As explained herein, according to the portable wireless unit ofthe invention, comprising a first plane antenna in a size having ahigher resonance frequency than the frequency of transmission andreception, a second parasitic plane antenna is disposed in the outersurface or inner surface of the case opposite to this plane antenna, andtherefore the antenna occupied area in the case is smaller, and theeffective antenna area can be increase by coupling of the second planeantenna, so that the case space can be utilized effectively, and theportable wireless unit is reduced in size and weight, and theaccommodating (mounting) efficiency is enhanced. Further, thecombination of the first and second plane antennas may function as oneantenna so as to have one resonance characteristic, and thereby theantenna characteristic may be enhanced.

[0039] Although the invention has been described with respect tospecific embodiment for complete and clear disclosure, the appendedclaims are not to be thus limited but are to be construed as embodyingall modification and alternative constructions that may be occurred toone skilled in the art which fairly fall within the basic teachingherein set forth.

What is claimed is:
 1. A portable wireless unit comprising: a firstplane antenna smaller than an antenna size determined by a desiredfrequency, and a second plane antenna presenting an antenna sizedetermined by said desired frequency on the whole by coupling with saidfirst plane antenna.
 2. The portable wiring machine of claim 1 , whereinsaid first plane antenna is disposed on a circuit board incorporated ina case as a casing.
 3. The portable wiring machine of claim 1 , whereinsaid second plane antenna is provided on outer surface or inner surfaceof the case as a casing.
 4. The portable wiring machine of claim 1 ,wherein said first plane antenna is a plate-form inverted F typeantenna, microstrip antenna, or chip antenna.
 5. The portable wiringmachine of claim 1 , wherein said first plane antenna has a narrow band.6. The portable wiring machine of claim 1 , wherein said first planeantenna is supplied with current, and said second plane antenna isparasitic.
 7. The portable wiring machine of claim 1 , wherein saidsecond plane antenna is disposed so as to be overlaid in a part or wholeon said first plane antenna.